Which of the following bacterium causes crown gall disease in plants? A. Bacillus thurigiensis B. Agrobacterium tumefaciens C. Pseudomonas fluorescens D. None of these

The correct answer is: B. Agrobacterium tumefaciens

Agrobacterium tumefaciens is a Gram-negative, rod-shaped bacterium that is capable of infecting dicotyledonous plants. It is the causal agent of crown gall disease, a plant disease that causes tumors to form on the roots and stems of infected plants.

A. Bacillus thurigiensis is a Gram-positive, rod-shaped bacterium that is used as a biopesticide. It produces a protein called Bt toxin, which is toxic to insects.

C. Pseudomonas fluorescens is a Gram-negative, rod-shaped bacterium that is a common soil bacterium. It is not known to cause any diseases in plants.

D. None of these is the correct answer.